Carrier-current signaling system



Nov. 10, 1925- E. v'. GRIGGS y CARRIER CURRENT s IGNALING SYSTEM Filed March 31. 192,5

r@ SQ PSEEEE /m/en/or .f5/mer V 6r/99s by Af/y .Patented Nov. 1o, 1925.

. UNT' STATES 1,561,227 PATENToI-*Fica ELMER V. GRIGGS, OF EAST ORANGE, NEW JEBSEY,.ASS1GNOR TO WESTERN ELECTRIC COMPANY,

INCORPORATED, 0F NEW YORK, N. Y., A CORPORATION 0F NEW YORK.

cAnnInnf-CIUBRENT .sxeNAmNe SYSTEM.

Application lcd March 31, 1923. Serial No. 628,987.

To all whom it may concern.: p

Be it known that I, ELMER V. Genies, a citizen of the United States of America, re'- siding at East Orange, in the county of 'EsseX and `State of .New Jersey, have invented certain new and useful llmprovements in Carrier-Current Signaling Systems, of which the following is a full, clear, concise, and exact description.`

' This'invention relates to a carrier current signaling system, and more particularly to a multiplex carrier current telegraph system employing speech frequency carrier cur-l rents.

An object of the invention is to increase y the. number of channels-within a given frequency range.

Another object is to simplify the apparatus required in such a syste Other objects and advantages will hereinafter appear.

According to the invention, the channels of a multiplex carrier telegraph system employing di'erent frequencies are separated ML 5 in groups by filters at the receiving terminal, the, channels of one group then being separated by selective circuits, and thechannel frequencies of each of the other groups first being reduced to produce frequencies corresponding to those of the rst mentioned group and then-separated by selective circuits like those employed in the firstgroup.

One of the advantages of a system em- 1bodying the invention is simplification of the receiving apparatus wherein thenumber of diderent kinds of selective circuits is reduced to the number of channels in kone group.

The factor limiting the number of channels of multiplex carrier waves which may be successfully appliedto a circuit of given frequency transmission range is the spacing or percentage frequency difference required between adjacent requencies to avoid interference. Features of the/present invention are, substantially uni-forinpercentage difference between adjacent frequencies which are to be separated, a decrease in the number of different designs of selecting circuits re- -quired and an increase in the number of available channels encompassed within a given frequency range.

While the invention is illustrated as applied to a multiplex carrier telegraph system employingl carrier currents of speech frequency,

it will be understood that it may also vbe applied to .multiplex carrier signalmg systems employing carrier currents of other frequencies of audio or higher than audio frequencies.

It is, of course not essential that thesystem have a ground return, for a full metallic circuit may be employed.'

In the drawings,

`Fig. 1 shows diagrammatically amultiplex carriertelegraph s rier currents of audio equencies Fig. 2 shows in detail one of the transmitting channels.

Fig. 3 shows in detail one of the receiving channels.

As shown in Fig. l, the multiplex carrier telegraph system comprises a'plurality of transmitting channels TLI, TL?, TLa, etc. located at one terminal and coupled to a main line ML, and a plurality of receiving channels RLl, RL2, EL3, etc. located at the other terminal and xcoupled to themain line As illustrated, there are twenty-five transmitting channels and a corresponding number of receiving channels.

These `channels may be divided into five groups, carrier frequencies of 200, 250, 310, 390 and 500 c cles bein assigned to the transmitting c annels o the first group. The carrier frequencies assigned ,to the transmitting channels of each of the other groups are respectively 400, 800, 1200 and 1600 cycles higher than those assigned to the 90 channels of the first group.

Each transmitting channel as shown in Fig. 2 includes an oscillation generator *Dl or other source-of carrier current of the frequency assigned thereto, a signal-trans! mitting element T1, an am lier TA1, and a `transmitting selective circuit TG1.

f The oscillation generator 0 of any well known type, such as a vacuum type oscil- `latorsupplies the carrier current for the channel. The .frequency of the generated carrier current may be changed by' a variable condenser l in the oscillator frequency determining, circuit 2. Variable resistance 1")`v determines the am litude of the oscillations fed back from t e oscillator outputto inputcircuit.-

The output circuit of the oscillator O1 lis coupled by means of a potentiometer 4 to the work circuit containing the signal transstem employing car-. i

mitting element or keyr T1. One contact of key T1 is connected to the control electrode of the amplifier TA1 which may be of any well known type such as, for example, a 'vacuum tube amplifier.

The transmitting selecting circuit TG1, coupling the amplifieroutput circuit to the main llne ML, comprises a transformer whose primary and secondary windings through the cooperation of condensers 5 and 6 are tuned to the carrier frequency assigned to the channel.

The receivin channels are coupled to the main line ML y band filters and frequency reducers.

Each band filter is of the type shown in Fig. 14 of the article by Colpitts and Blackwell entitled Carrier current telephony and telegraphy appearing in Transactions of American Institute of Electrical Engineers vol. 40, 1921. When used in the present system, one of the input terminals of each o the band filters is grounded.

The band filters separate the channels into five groups corresponding to the frequency grouping of the channels at the transmitting terminal.

Each of the band filters is designed to pass carrier currents of the frequencies assigned to the channels of a particular group and the side band frequencies thereof and to suppress currents of all other frequencies.

Thus band filter BF1 is designed to pass only the carrier currents of 200, 250, 310, 390 and 500 cycles assigned to the five channels of the first group and currents of frequencies within the side bands of these carrier frequencies. f

The frequency reducers FB2, FRS, FR4r and FR, reduce -the frequencies of the in coming signal currents transmitted from the channels of groups 2 to 5, so that the signal currents assing to the receiving channels of each of)theseV groups are of the same freuencies as those passing to the receiving c annels` of the first group.

Each frequency reducer may be of any 1..'

receiving terminal are selected by the band well known type such as, for example, the vacuum tube frequency reducer D1 disclosed in U. S. Patent 1,361,487 granted December 7, 1920 to H. S. Osborne.

Incoming signaling currents of the frequencies selected by a band filter are 1mpressed upon its associated frequency reducer wherein they react with locally supplied oscillations and produce currents of frequencies which are the difference between the frequencies of the incoming and the locally sup lied currents.

The local) nished from a harmonic generator 10 or any other suitable source or sources.

The harmonic generator or producer 10 may be of any well known type, such as, for

example, a vacuum tube harmonic producer lysupplied currents-may be furlsimple series tuned circuits composed of' capacity and inductance proportioned to tune the circuit to currents of the frequency to be selected and supplied to its associated frequency reducer. a

Each of the receiving channels contains a selective circuit RC1, an amplifier RA1, a rectifier R1, and a receiving relay RR1.

Each selecting circuit RC1 comprises a transformer whose rimary and secondary windings through tie cooperation of condensers 7 and 8 are tuned to currents of the frequency to be received by the receiving channel with which it is associated. The transformers and their associated condensers form a tuned coupling between the main line and the respective receiving channels.

The currents of the frequencies selected by the selecting circuit RC1 are impressed upon the amplifier RA, coupled to the rectifier\R1 by means of a potentiometer 9 for regulating the magnitude of the amplified currents delivered to the rectifier.

The receiving relay RR1 in the output cir cuit of the -rectifier R1 is responsive to the rectified currents and controls a sounder 11 or other signaling device.

The operation of the system is as follows:

Assuming that the transmitting key T1 of transmitting channel TL1 is operated to form and transmit marking and spacing signals, 200 cycle currents are impressed upon amplifier TA1 each time that key T1 is closed. The amplified currents pass through the tuned coupling TG1 to the main line.

The transmitted Signal currents having originated in a transmitting channel of the first group, such currents incoming at the filter BF1. These signal currents after passing through the band filter BF1 are selected by the tuned coupling RC1 of receiving channel RL1.l The signal currents so se1ected are impressed upon amplifier RA1, and the amplified currents therefrom are then impressed upon the rectifier R1. Receiving relay RR1 in responding to the rectified currents causes the operation of the associated sounder 11.

If the signals are transmitted from a transmitting channel of any group other than the first group, for example, from transmitting channel TL111 of the third group, the signal currents incoming at the receiving terminal are selected by the band filter BF1.

-The selected currents passing through the band filter BF3 are impressed upon the frequency reducer FR3, wherein the 1100 cycle signal currents interact with the locally supplied 800 cycle currents and produce' 310 cycle currents. The difference frequency 310 cycle currents are selected by the selective circuit RC13 of the receiving channel 'lille selected. 310 cycle currents after being amplified and rectified cause the operation `of the receiving relay RRwl which in turn operates the sounder associated therewith.

It will be observed that in the system illustrated, it is possible to obtain twenty-five channels with approximately twenty-five percent discrimination in the receiving channels. The selecting circuits of the receiving channels of one group are like those employed in each of the other groups, thereby reducing the number of different receiving channel selecting circuits to five.

The frequency spacing between'adj-acent groups is 100 cycles. Should it be desired to obtain greater frequency spacing between adjacent groups, the fifth channel of each group maybe omitted, thus providinga 210 cycle spacing of adjacent groups.

The invention set forth herein is,l of course, susceptible of various other einbodi- ,ments and adaptations.

The invention claimed is: v

1. The method of receiving signals in a multiplex carrier signalingv system, which comprises separating the incoming signal oscillations of different carrier frequencies.

into groups, separating the signal oscillations of one group and impressing them upon` signal receivers, reducing the frequency of the signal' oscillations of each of the other groups, and separating such signal oscillations of reduced frequency and impressing them upon signal receivers.l

2. The method of receiving signals in a multiplex carrier signaling system, which comprises separating the incoming signal oscillations of different carrier frequencies into groups, selecting-the signal oscillations of one group and impressing them upon signal|` receivers, stepping down the frequencies of .the signal oscillations of each of the other groups to the frequencies of. the first group of signal oscillations, selecting such signal oscillations of stepped down frequencies, .and impressing such selected signal oscillations upon signal receivers.

3. In a multiplex carrier signaling system wherein a plurality of receiving channels are coupled toa main line to receive incoming signal oscillations of dierent frequencies the combination of selective circuits between the main line and thereceiving channels to separate the incoming signal oscillations into groups according to the frequency thereof and thereby separating the receiving sponsive to oscillations channels into groups, a selective lcircuit in Il each channel of one group to select the incoming signal oscillationsof frequencies assigned thereto, a frequency reducer for each of the other groups supplied with local oscillations to step down the frequencies of the incomin signal currents selected by the group selecting circuit associated therewith u selective circuits in the channels of `each of said last mentioned groups to select the currents of stepped down frequencies, and a signal receiver in each receiving channel reof ythe frequency selected by the selecting circuits thereof.

4. In a multiplex carrier signaling system comprising a main line a plurality of'transmitting channels employing carrier-oscillations of different frequencies located at a terminal station and coupled to the main line, a signal transmitter for each channel, a plurality of receiving channels located at a distant terminal station, a plurality of selective circuits between `the main line and the receiving channels to separate the receiving channels into groups according to the carrier frequencies assigned to the transmitting channels, aselective circuit in each receiving channel of one group, a frequency reducer for eachof the other groups supplied locally with oscillations Whereby the frequencies of the signal currents selected by the group` -selecting circuit Vassociated therewith are reduced to frequencies corresponding to those of the signal vcurrents received in the channels of the first group, selective circuits like those of the first group 100 of receiving channels for the receiving channels of each of the other groups, and a signal receiver for each receiving channel responsive to currents of the frequency selected by the selective circuit thereof. l05

5. The combination in a multiplex carrier wave transmission system in which the entire frequency range encompassed is divided into a plurality of groupskthe lower frequency group having carrier frequencies U0 such that each differs from its adjacent frequencies by 'substantially the saine percentage that any other differs from its adjacent frequencies and each of the other groups having a set of frequencies differing respecl5 tively from those of said lower frequenc group by a dierence frequency substantially constant for that particular group of means for separating currents into groups corresponding to said frequency groups, and means for modifying the frequencies of currents of a given group to a different and definite relation to the frequencies of another group. v. l

In witness whereof, l 'hereunto subscribe m5 my name this 27 day of March A. D., 1923.

ELMER V. GRIGGS. 

